Rebuilding a 400.

[Mopar_Shmopar]

I have a 1973 Roadrunner, and I’m finally getting to the point where I’m ready to rebuild the engine and trans. The transmission is already out for a rebuild, but I’d like to tackle the engine rebuild myself.


That said, most places I’ve asked haven’t been too helpful—99% of the responses are, “Why bother with the 400? Just get a 440.”


Sure, I could do that. But I don’t want to. This car is numbers matching, and more importantly, it was a project my dad and I were supposed to do together. He passed away before we ever got the chance to dig in, so finishing this the right way means a lot to me. I want to keep the original 400 block and do it right.


My experience is mostly with Fords—specifically Coyotes—and I’ve done a fair amount of work on my ‘69 F250 (rebuilt heads, timing job, etc.). But Mopar stuff is uncharted territory, especially when it comes to engine internals and aftermarket parts.

Here’s what I want to achieve:​

1. Around 400 crank HP. If that’s not possible in my budget, I’m okay going lower, but I want a solid step up from stock.
2. I want the engine to be reliable enough for daily driving, with the strength to take hard driving without breaking.
3. I want to keep the engine carbureted.
4. I want to stay under $5,000 for the engine build (not including the trans).

Based on research, here’s what I think I need:

• The 400's stock compression is super low, so I know I’ll need new pistons.
• The factory iron heads are pretty weak—aluminum heads seem like a good upgrade.
• I’ve read that stroking the 400 with a 440 crank is a relatively simple and affordable way to add displacement and torque.
• I’ll likely need to bore it .030 or .040 over.
• The stock exhaust manifolds aren’t ideal. Most people I’ve talked to recommend long tubes.

Does any of that sound off base? Has anyone here built a 400 for similar goals?
Also, are there any brands you trust or ones I should absolutely avoid?


Any advice would mean a lot. I want to build something my dad would’ve been proud of.

 

[icetech]

The 400 is a great motor that was made at the wrong time, low compression.. smog ****.. it just was crippled from the start.. I ran one in my challenger for 8 years (then sold it.. still ran perfect after a lot of beatings) At the time i had no money... i Milled the heads .100 to bring up compression and used a .484 purpleshaft (LOVED that cam).. headers/intake and normal stuffs... If you are on a budget but plan on aluminum heads (good call) check combustion chamber CC on aftermarket heads.. you might get away without changing pistons..

On my 400, i did a quick hone, new bearings/rings and zero issues. Being like 22 at the time.. had no cash for a full on rebuild but never regretted just doing a quicky on it.

 

[icetech]

BTW... Mopar big block stuff is easy to get, hit facebook market place for a intake and other bits...

And in case you don't know.. your 400 is a "low deck" 426/440 are "Raised deck".. the intakes don't interchange so make sure to get a 383/400 intake. Other than that it's all pretty much the same (someone will let you know if i'm wrong bout that, been a long time)

If you get work done on the block and they do cam bearings, make sure a cam fits and spins freely before you take it home.. Mopars have cam bearing issues and if the guy isn't a mopar guy he won't know. Also.. the 4th bearing feeds oil to the top end, the bearing has 3 holes that have to line up with the block or no oil to the top.. just a mopar thing to make sure to check.

Only reason i mention the bearing thing is when i had my block done the guy didn't line up the holes, then tried to say i spun the cam bearing while putting the cam on... Really?

400 is a great motor.. 400hp is jut 1hp/cube.. literally heads/cam/intake would do that.

 

[RemCharger]

First of all, welcome to the board, and sorry to hear about your father. Glad to see you are following through with the project he would be proud. Please introduce yourself in the welcome wagon.

I have a 1973 Roadrunner, and I’m finally getting to the point where I’m ready to rebuild the engine and trans. The transmission is already out for a rebuild, but I’d like to tackle the engine rebuild myself.


That said, most places I’ve asked haven’t been too helpful—99% of the responses are, “Why bother with the 400? Just get a 440.”


Sure, I could do that. But I don’t want to. This car is numbers matching, and more importantly, it was a project my dad and I were supposed to do together. He passed away before we ever got the chance to dig in, so finishing this the right way means a lot to me. I want to keep the original 400 block and do it right.


My experience is mostly with Fords—specifically Coyotes—and I’ve done a fair amount of work on my ‘69 F250 (rebuilt heads, timing job, etc.). But Mopar stuff is uncharted territory, especially when it comes to engine internals and aftermarket parts.

Here’s what I want to achieve:​

1. Around 400 crank HP. If that’s not possible in my budget, I’m okay going lower, but I want a solid step up from stock.
2. I want the engine to be reliable enough for daily driving, with the strength to take hard driving without breaking.
3. I want to keep the engine carbureted.
4. I want to stay under $5,000 for the engine build (not including the trans).

Based on research, here’s what I think I need:

• The 400's stock compression is super low, so I know I’ll need new pistons.

• The factory iron heads are pretty weak—aluminum heads seem like a good upgrade.

the factory heads are actually quite a bit stronger, thanks to the iron. I think you're trying to say 60 yr newer heads have better ports on average, due to long term technology advancements - that's fair

• I’ve read that stroking the 400 with a 440 crank is a relatively simple and affordable way to add displacement and torque.

It involves completely re- machining the crank, making it weaker at the same time. Thus making your # s matching block a time bomb. When, who knows. Simple, no. Affordable ? Depends how thick the wallet is.

• I’ll likely need to bore it .030 or .040 over.
• The stock exhaust manifolds aren’t ideal. Most people I’ve talked to recommend long tubes.

Does any of that sound off base? Has anyone here built a 400 for similar goals?
Also, are there any brands you trust or ones I should absolutely avoid?


Any advice would mean a lot. I want to build something my dad would’ve been proud of.

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Here would be your first reading assignment. Lengthy, but all inclusive..
Thread 'My new stock stroke 400 build' My new stock stroke 400 build

 

[icetech]

Last thing from me... Look at 440source for parts.. they sell complete Aluminum heads for $699 each which is absolutely insane (i wish they would do a 360source store also) They also have good prices on other parts you might need

 

[496 polara]

Welcome! You are already making dad proud.

First I would asses what you have, what is usable and what is not as is. The more you can use/re-use the more $$$ available to spend on upgrades.

I like a 400 engine. Low compression and all. Have one in my 72 Newport I hope to get around to one day. A blueprinted 400 magnum engine makes a good pump gas street engine and I think 400hp is easily attainable.

The slug 400 on the dyno.

 

[69conv]

What I did with my 400. Bored 40 over which let me use 440 pistons.. Gave me a huge selection and allowed me to raise my compression ratio from the basement. Put on 440 source heads which increased flow and lightened the front of the car by a good 50 lbs. I used a Performer rpm intake to help flow and lightened the front still more, and topped it off with a 850 street demon. 415 hp and 515 torque. Oh yeah, I called Schneider cams and had them grind me a cam to spec. In case you didn't know, Schneider cams developed the original purple shaft cam series and sold the to mopar. Good luck with your build!

 

[69conv]

 

[qkcuda]

I built a 400 about 20 years ago and it made 415 HP and 450 TQ. The one I just built that RemCharger referred to above made 340 HP and 420 TQ. The only significant difference was the cam choice. Your goals are easily reachable with a stock stroke build. The first engine was still very streetable.

 

[RemCharger]

My street 383 .030 has a 284xe cam, 516 heads. Always figured it was around the 425 mark. Ran 13.1 at 105 in a 4000lb 67 Charger

 

[LSS&B]

Hughes Engines Whiplash cam gives a big performance boost if you decide not to bore and replace pistons.
Specifically made for low compression engines.
$600, kit is a deal. Whiplash link below.
https://www.hughesengines.com/Index...V2hpcGxhc2ggTXVzY2xlIENhciBDYW1z&partid=31306
Welcome and good luck!

 

[Mopars & Missiles]

Definitely build the 400, its a great engine when built correctly. The 400 has less valve shrouding (due to a larger bore) than a 440, making it breathe much better which of course lends itself to more power output.

I chose to stroke my 400 block with an Eagle 4.15" crank, resulting in 499 cu. in. at stock bore. Unbelievable torque and instantaneous throttle response with an 850 cfm carb up top. I used edelbrock aluminum heads and intake back when I built it. There may be better choices available now, such as trick flows, etc.? I used Eagle H beam rods, Icon forged pistons, Total Seal rings, Clevite bearings, Hughes Hyd. flat tappet 3 bolt cam, etc., etc. While I've never had the engine on a dyno, I suspect its very near or over 600 HP and easily that much or more torque (at the crank).

Of course I spent a bit more than what you have budgeted for your engine and that was 11 years ago when prices were cheaper than today, so keep that in mind. Regardless, I say build that 400 matching numbers engine and run it like you stole it!

My finished engine before and after installation in the car.

 

[QuickBpBp]

First sorry to hear about your Dad but nice to see you continuing with the project. My advice is RESEARCH everything before you buy so you can stay with in your budget of 5K as parts and machining costs have gone through the roof these days unless you know someone who can help you out. That will help you from having new stuff laying around that you can't use...

 

[Demonic]

Nothing wrong with the later 70's castings, ports are similar to the 906 heads. The question is how worn are they? If you need 8 exhaust guides and the obligatory light cut on the surface, modern costs can approach a set of aluminum heads.

 

[Mopar_Shmopar]

Welcome! You are already making dad proud.

First I would asses what you have, what is usable and what is not as is. The more you can use/re-use the more $$$ available to spend on upgrades.

I like a 400 engine. Low compression and all. Have one in my 72 Newport I hope to get around to one day. A blueprinted 400 magnum engine makes a good pump gas street engine and I think 400hp is easily attainable.

The slug 400 on the dyno.

The engine appears to have been rebuilt at one point, as the block was painted Ford Blue. I've already torn the engine apart and am waiting to get it sent in to be cleaned and machined. The crank has some visible wear, and the pistons look stock. The heads don't look awful, just grimy, yet then again, I don't know what to look for. Should I send the crank and heads in with the block as well? I don't know how many miles the car is on as the speedo was broken when we bought it. ODO is stuck at 98,000ish iirc.

 

[icetech]

The engine appears to have been rebuilt at one point, as the block was painted Ford Blue. I've already torn the engine apart and am waiting to get it sent in to be cleaned and machined. The crank has some visible wear, and the pistons look stock. The heads don't look awful, just grimy, yet then again, I don't know what to look for. Should I send the crank and heads in with the block as well? I don't know how many miles the car is on as the speedo was broken when we bought it. ODO is stuck at 98,000ish iirc.

Mopar also painted motors blue... I would find out the cost to go through heads and if it's more then like 60% of the 440source heads.. get the new heads. If the crank journals all look good without scoring i would probably just run it, but that's me.. those cranks are very tough and in a stock motor like that it never saw much stress

 

[hunt2elk]

Stroked 400's are great motors, I have 2 of them. I vote for buying a stroker kit from 440 Source, especially since you are already needing new pistons. Pretty good bang for the buck.

 

[moparedtn]

Stroked 400's are great motors, I have 2 of them. I vote for buying a stroker kit from 440 Source, especially since you are already needing new pistons. Pretty good bang for the buck.

Yep. I'd recommend checking out a channel on YouTube called JustMoparJoe. He has a lot of experience building 400's
(especially stroked ones) and along with our fellow FBBO member @rickseeman cranks out some serious machinery.
The 400 in some ways is actually a superior base to work off of to the 383.

 

[icetech]

Yep. I'd recommend checking out a channel on YouTube called JustMoparJoe. He has a lot of experience building 400's
(especially stroked ones) and along with our fellow FBBO member @rickseeman cranks out some serious machinery.
The 400 in some ways is actually a superior base to work off of to the 383.

Love his videos.. i wish Rick was local.. i would like to see his face when i ask him to do a small block for me when he has 20 hemis laying around

 

[HawkRod]

The engine appears to have been rebuilt at one point, as the block was painted Ford Blue. I've already torn the engine apart and am waiting to get it sent in to be cleaned and machined. The crank has some visible wear, and the pistons look stock. The heads don't look awful, just grimy, yet then again, I don't know what to look for. Should I send the crank and heads in with the block as well? I don't know how many miles the car is on as the speedo was broken when we bought it. ODO is stuck at 98,000ish iirc.

A couple of random thoughts here:
1) As others have said, the 400 is a great engine - keep it - it can easily meet your goals.

2) If your crank and pistons need work, then maybe consider a stroker kit if your budget allows. I have a 500 CI 400 based stroker and it makes 675 lb feet of torque. It is a joy to drive around town because lots of that torque is at low RPM. But even if you keep your stock stroke, my suggestion is to build for low end torque rather than high end horsepower - this will make for a much better street engine.

3) Spend time and money on the machining of your block. Make sure your mains are within spec, have no taper and are straight. You need this to make sure your crank spins freely and that you don't spin a bearing. It is crush that keeps bearings from spinning, so the specs of your mains (and rods) is critical. Don't just assume that they are OK. For example, a brand new set of rods I got for my 340 stroker were (just) out of spec right out of the box! Additionally, the unfortunate truth is Mopar factory machining sucked sometimes. Check the deck height of your block and get it corrected if it is more than about .002" off. Many Mopar blocks are off by more than .010", and this creates uneven compression.

4) For the heads: The valve guides and seats are important to check. Remove the springs and visually inspect the seats. You should see a nice, even, clean ring. If there are any breaks or it looks worn, the seat needs work. For the valves, try the wiggle test. There should be roughly .002" clearance between the valve guide and valve stem. Take the valve (loose, in your hand) and insert it into the guide. Then try to wiggle it in all clocking positions. It should barely wiggle (but it should have definite movement - hard to describe in words). Do this to all valves and you may likely feel a couple that wiggle a lot. If they do, then you need your guides either reconditioned or replaced. Finally, take a straight edge and lay it across your heads. See what size feeler gauge you can put under the straight edge, especially in the center of the head. If more than .002" or .003", then your heads should be resurfaced.
As others have said, if your heads need extensive work then aluminum heads are a great upgrade. Technology has changed a lot over the years and the new aluminum heads breathe much better, giving you a lot more power.

5) The crank and mains are partners. So the size of your crank and mains must work together and ideally have roughly .0025" clearance. So when your block is machined and prepped, your crank should be checked as well. It might need to be turned, and then you need different bearings. Same is true for your rod throws.